Ectomycorrhizae and Their Importance in Forest Ecosystems

Abstract

Ectomycorrhizal (ECM) associations involve the most diverse category of myocrrhizae. The diversity derives from the fungal partners; more than 5,000 species of fungi, mainly Basidiomycetes, with a limited number of Ascomycetes and Zygomycetes, make the relationship very diverse. On the contrary, however, relatively few families of plants such as Fagaceae, Pinaceae, Betulaceae, and Dipterocarpaceae are involved in the ECM associations. These plants, however, are distributed over wide areas of temperate and boreal forests, and are therefore economically important. ECM fungi make associations with plants by forming a sheath (mantle) around fine root tips with hyphae that grow inward between root cells of the cortex and make Hartig net, and emanate outward through the soil, increasing the surface area to absorb nutrients and water. Thus, the mycorrhizal fungi gain photosynthates and other essential substances from the plant and in return help the plant take up water and minerals. Pine wilt disease (PWD) is a globally serious forest disease, and also shows the importance of ectomycorrhizal relationships. Pine trees planted on a mountain slope were killed by PWD, but some trees survived at the top of the slope, where mycorrhizal associations developed far better than on lower slopes. ECM associations, beside fertilization, also increase the supply of water to the pines, and elevate host resistance against disease and parasites. Moreover, inoculation of pine seedlings with ECM fungi under laboratory conditions confirmed the increase in their resistance to PWD. Pine seedlings can tolerate the adverse effects of environmental stress such as acid mist when infected with ECM fungi. These fungi can also make a significant contribution to forest ecosystems by increasing biomass and creating a network among trees through which nutrients may transported. ECM fungi also improve the growth of host plants at the seedling stage. Many pioneer plants in wastelands are facilitated in their establishment by ECM. This association has been successfully applied to reforestation programs in tropical forests by inoculating mycorrhizae on to nursery seedlings.

References

Abuzinadah, R.A., and Read, D.J., 1986, The role of proteins in the nitrogen nutrition of ectomycorrhizal plants. I. Utilization of peptides and proteins by ectomycorrhizal fungi. New Phytol. 103: 481-493.CrossRefGoogle Scholar

Dosskey, M.G., Boersma, L., and Linderman, R.G., 1991, Role for the photosynthate demand of ectomycorrhizas in the response of Douglas fir seedlings to drying soil. New Phytol. 117: 327-334.CrossRefGoogle Scholar

Finlay, R.D., and Read, D.J., 1986a, The structure and function of the vegetative mycelium of ectomycorrhizal plants. I. Translocation of carbon-14 labeled carbon between plants inter-connected by a common mycelium. New Phytol. 103: 143-156.CrossRefGoogle Scholar

Finlay, R.D., and Read, D.J., 1986b, The structure and function of the vegetative mycelium of ectomycorrhizal plants. II. The uptake and distribution of phosphorus by mycelial strands interconnecting host plants. New Phytol. 103: 157-166.CrossRefGoogle Scholar

Harley, J.L., and McCready, C.C., 1952, The uptake of phosphatase by excised mycorrhizal roots of the beech. III. The effect of the fungal sheath on the availability of phosphate to the core. New Phytol. 51: 342-348.CrossRefGoogle Scholar

Jones, M.D., and Hutchinson, T.C., 1986, The effect of mycorrhizal infection on the response of Betula papyrifera to nickel and copper. New Phytol. 102: 429-442.CrossRefGoogle Scholar

Jones, M.D., Durall, D.M., and Tinker, P.B., 1991, Fluxes of carbon and phosphorus between symbionts in willow ectomycorrhizas and their changes with time. New Phytol. 119: 99-106.CrossRefGoogle Scholar

Kennedy, P.G., Izzo, A.D., and Bruns, T.D., 2003, There is high potential for the formation of common mycorrhizal networks between understorey and canopy trees in a mixed evergreen forest. J. Ecol. 91: 1071-1080.CrossRefGoogle Scholar

Read, D.J., 1992, The mycorrhizal fungal community with special references to nutrient mobilization. In: Carrol G.C., and Wicklow D.T., eds. The Fungal Community: Its Organi-zation and Role in the Ecosystem. New York, Marcel Dekker, 631-654.Google Scholar